The proposed continuation of an established program provides training at the postdoctoral level in immunobiological, immunochemical, immunogenetic concepts and techniques with special emphasis on the study of problems related to the immune and the a1lergic response in pediatrics. The faculty of the Division of A1Iergy/Immunology/Rheumatology and of the Howard Hughes Medical Institute and Gene Therapy Laboratories at Children?s Hospital/Department of Pediatrics at Harvard Medical School, has particular competence in the study of cell interactions, immunoglobulin gene rearrangement, immune deficiency diseases, mechanisms of T ce1l activation, animal models of immune deficiency, mechanisms of human IgE regulation and gene therapy. The training program consists of a three-year research experience. Support is requested for nine postdoctoral trainees having either an M.D. or Ph.D. degree or both and having had zero to three years of biomedical experience before entering the program. For M.D.s the program offers integrated training with a year of intensive training in clinical allergy/immunology/rheumatology, supported through clinical funds, followed by three years of research. The program, in its fifteenth year, continues to fulfill a need to train physician scientists in pediatric allergy/immunology/rheumatology, including members of underrepresented minority groups, with virtually all graduates supported by the Training Grant occupying academic positions.